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C compilation optimization: deleted unedited parts on the fly

We are faced with an interesting topic. Suppose we have a special-functions.c file, basically a library. We need to optimize the code by getting rid of all unused / unaccounted functions during the build process on the fly. I'm not looking for unused (dead) code at all: some parts will be “dead” if compiled to one of the architectures, but they will be used in another architecture assembly.

Does anyone know flags, tools, methods, and tricks? The compiler is a standard gcc with the code ansi 99 C.

EDIT I ​​know this is basically part of the linker, but using gcc the process is not split into two parts.

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3 answers

From http://embeddedfreak.wordpress.com/2009/02/10/removing-unused-functionsdead-codes-with-gccgnu-ld/ :

  • Compile with -fdata-sections to save data in separate section data and -ffunction-sections to save functions in separate sections, so they (data and functions) can be discarded if they are not used.
  • Link to --gc-sections to delete unused partitions.

For instance:

 gcc -Os -fdata-sections -ffunction-sections test.c -o test -Wl,--gc-sections
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I think the recent GCC (i.e. 4.6 ) should do this if you compile and link the -flto flag (link time optimization). I would suggest that having hidden or internal visibility should be relevant (at least for non-static functions).

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As far as I know, GNU binary utils (ld, in this case) already remove unusesd links by static link

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Source: https://habr.com/ru/post/1384068/

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